Ideally used for this kind of retractable system: http://hobbyking.com/hobbyking/store/__12883__Digital_Servoless_Retractable_system_1pc_.html Feel free to adapt it to any use (even without retracts). Can be used with a gimbal on the bottom, just drill where you need and attach. Split into 4 parts for easier printing. Glue with epoxy or any other strong glue. Tip: For weight saving, use around 3% infill.